Various noxious gases are major environmental pollution problems. Ozone and nitrogen oxides (NOx) are the two principal oxidants produced that are responsible for air pollution. Ozone is present in the stratosphere where passenger planes fly and it is also generated by electrophotographic equipment and ozone sterilizers that use a corona discharge lamp. Excess ozone must be removed. Various effects of ozone on human health are described in "Kasseitan Kogyo" (Activated Carbon Industry), Jukagaku Kogyo Tsushin-sha Publishing Company, 1974.
Several materials have been proposed for removing noxious gases, particularly ozone in air and exhaust gas, by adsorption or decomposition, but none of them are completely satisfactory. For example, ozone removers or decomposers in the form of a catalyst of Mn, V, Fe, Cu, Ni, Cr, Co and Zn oxides or salts thereof on granular or powdery activated carbon carriers, or of a decomposition catalyst made of these elemental metals are known, but their efficiency in removing ozone is not high and they are not considered to be very good ozone removing materials. A material made of Pd or Ag supported on granular activated carbon has been proposed, but it has low ozone removing efficiency and is short-lived; furthermore, Pd or Ag are costly metals. Another type of filter comprises a container simply filled with powdery or granular activated carbon, but if the linear velocity of the gas treated is high, the powdery or granular activated carbon scatters, blows off or undergoes channelling, which causes excessive wear of the carbon and fouls the treating system.